It seems harmless enough, but the strange sight was enough to raise suspicion in one eagle-eyed fisherman.

Had the fisherman taken them home, instead of to the Rockhampton Police Station, two men who survived a helicopter crash may have died before rescue.

Acting Inspector Ben Carroll, from Rockhampton Police, said officers had no clues as to what had unfolded near Curtis Island when the man bought the esky and rods into the station on Saturday afternoon.

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A strong smell of fuel on the items raised more concerns, so the Rockhampton search and rescue coordinator took over the investigation.

The RACQ Capricorn Helicopter Rescue Service was called in and on Saturday afternoon found a suitcase on Curtis Island, about 60km south-east of Rockhampton.

It wasn't until police called the phone numbers located in the luggage they realised a helicopter was involved.

Act Insp Carroll said the relatives they spoke to hadn't realised anything was wrong, but police suspected something serious had happened.

Aircrew using night vision goggles had been conducting a second search flight around 10pm focussing on an area near Keppel Creek when they found the chopper.Gavin Lock

Police again called in RACQ Capricorn Helicopter Rescue Service, which found the Bell 206 JetRanger helicopter lying on its side in mud flats on Curtis Island around 10pm.

Two men, a 56-year-old from Margate and a 61-year-old from Scarborough, were found on a nearby beach in a critical condition.

The 61-year-old pilot suffered spinal injuries and was immediately airlifted to Rockhampton Hospital, before being transferred to Brisbane on Sunday.

Act Insp Carroll said a RACQ Capricorn Helicopter Rescue Service crew member stayed with the severely dehydrated passenger on the island while the pilot was taken to Rockhampton.

"Just by looking at the state of the aircraft in the mud flats, they were very lucky to survive," he said.

"They'd been there a long time and open to the elements.

"We were very fortunate the gentleman from the public noticed those items and then brought them into us because it could have been some time until relatives of the people on board became aware of what had happened.

"Another day may have passed.

"Had that member of the public not alerted us to the fact those items were there, we certainly wouldn't have commenced our search any earlier."

The scene of a helicopter crash on Curtis Island, where two men were lucky to survive after they were found more than a day after the crash. The men were found with these items on a beach, away from the mud flats where the chopper crashed.Contributed

It's understood the aircraft left Caboolture about 12pm on Friday and crashed that afternoon.

Act Insp Carroll said it was not known why it took so long to raise the alarm.

An RACQ Capricorn Helicopter Rescue Service spokesman on the weekend said the aircraft was carrying a personal distress beacon, but couldn't activate it as it was submerged with the helicopter.

Act Insp Carroll said the initial talks with the survivors suggested engine failure could have caused the crash, but the investigation was now in the hands of the Australian Transport Safety Bureau.

The helicopter remains on Curtis Island, with the owner and their insurance company responsible for its removal.